Encoder

ABSTRACT

A sealed encoder module for mounting onto a machine so as to measure relative displacement of first and second parts of the machine. The sealed encoder module can comprise, a scale, a readhead comprising a scale signal receiver, and an integral protective housing which encapsulates at least the scale and said scale signal receiver. The sealed encoder module can be configured to determine and output diagnostic information regarding a scale signal detected by the readhead.

This invention relates to an encoder apparatus. For instance, theinvention relates to what is commonly known as a sealed encoder, alsocommonly known as an enclosed encoder.

Encoders are used in many industries to provide position (or itsderivatives, e.g. velocity and/or acceleration) feedback to a controlsystem of a machine, e.g. feedback control for the position/motion ofone part of a machine relative to another part of the machine. As willbe understood, typically a scale is provided on one part of the machineand a readhead for reading the scale is provided on the other part ofthe machine such that the relative position of scale and readhead, andhence the relative position of the machine parts, can be detected by thereadhead along the encoder's measurement dimension.

The technologies utilised by such encoders can require that theenvironment in which they are used is clean and free of contamination,e.g. dust, dirt and moisture (which could, for example, be oil and/orwater based). Contamination on the scale and/or readhead can adverselyaffect the performance of the encoder. In many industries such machinesthat use encoders operate in an appropriately clean environment, inwhich case what is commonly referred to as an “exposed encoder” (or“open encoder”) can be used. Readheads of exposed/open encoders cancomprise a visual set up indicator (e.g. see the TONiC™ and RESOLUTE™encoders available from Renishaw plc, and see also U.S. Pat. Nos.5,241,173 and 8,505,210).

However, there are instances, such as in the machine tool industry forexample, where the working environment is not clean, and where fluidsand solid debris are prevalent. In such cases there can exist the needto protect the scale and readhead of an encoder against such detrimentalenvironments. As is known, this can be achieved by placing a cover overan installed exposed/open encoder, such as over a TONiC™ or RESOLUTE™encoder available from Renishaw plc, so as to provide a sealed barrierwhich protects the scale and readhead from such contamination. However,typically, in these circumstances, a different type of encoder is usedwhich is commonly referred as a sealed (also known as enclosed) encoder.Such sealed/enclosed encoders comprise a scale and a readhead, with anintegral protective housing which encapsulates the scale and at least ascale signal receiving part of the readhead, and which together areprovided and installed as a single module.

The present invention provides an improved encoder apparatus. Inparticular, the present invention relates to improvements to sealedencoders. For instance, according to the present invention there isprovided a sealed encoder module comprising a scale, a readhead and aprotective housing (e.g. an integral protective housing).

According to a first aspect of the present invention there is provided asealed encoder module for mounting onto a machine so as to measurerelative displacement of first and second parts of the machine in ameasuring dimension/degree of freedom (which could be linear or rotaryfor example). The sealed encoder module can comprise, a scale, areadhead comprising a scale signal receiver, and a protective housingwhich encapsulates at least the scale and said scale signal receiver.The sealed encoder module can be configured to determine and outputdiagnostic information. The diagnostic information could be indicativeof the relative arrangement of the scale and the scale signal receiver,in particular in at least one dimension/degrees of freedom other thanthat of the measuring dimension/degree of freedom of the encoder module.Accordingly, the diagnostic information could be dependent on therelative arrangement of the scale and the scale signal receiver, inparticular in at least one dimension/degrees of freedom other than thatof the measuring dimension/degree of freedom of the encoder module. Thesealed encoder module can be configured to determine and outputdiagnostic information regarding a scale signal detected by thereadhead. Accordingly, as explained in more detail below, the scalesignal detected by the readhead could be dependent on the relativearrangement of the scale and the scale signal receiver in at least onedimension/degree of freedom other than that of the measuringdimension/degree of freedom of the encoder module. As will beunderstood, the encoder module (e.g. the readhead) is also configured todetermine and output information concerning the relative position of thescale and readhead (i.e. position information, that is in the measuringdimension/degree of freedom). Accordingly, the encoder module can beconfigured to determine and output both position and diagnosticinformation.

Determining and outputting diagnostic information has been found to beparticularly useful for monitoring the performance of a sealed encodermodule and/or for aiding the installation/set-up of a sealed encodermodule; e.g. for those sealed encoder modules which have a scale signalreceiver which is arranged independently of the scale, described in moredetail below.

Accordingly, the sealed encoder module can comprise at least oneprocessor configured to determine said diagnostic information. As willbe understood, processors can include bespoke processors configured forthe specific application (e.g. a field programmable gate array “FPGA”)as well as more generic processors which can be programmed (e.g. viasoftware) in accordance with the needs of the application in which it isused. The at least one processor can be configured to analyse the scalesignal detected by the readhead to determine said diagnosticinformation. The, or another, at least one processor can be configuredto control output of said diagnostic information. For example, the, oranother, at least one processor can be configured to control theoperation of an output device (e.g. a visual output device) on the basisof the outcome of said analysis of the scale signal. The position anddiagnostic information can be determined by the same or differentprocessors.

As will be understood, the encoder module could be configured such thatthe diagnostic information determined and output can compriseinformation concerning the quality of the scale signal detected by thereadhead. The diagnostic information could provide a measure of thesuitability of the representation to provide position information (e.g.in the measuring dimension/degree of freedom); and in particular forexample reliable and/or accurate position information. Outputting saiddiagnostic information could comprise providing an output based at leastin part on at least one parameter determined as a result of a processconfigured to analyse the quality of the scale signal. For example, thecontrol of an output device, such as a visual output device, can bebased on said at least one parameter.

The diagnostic information output could be restricted to one of aplurality of predetermined categories. Such categories could representdifferent levels of quality of the detected scale signal. For example,the diagnostic information could be restricted to indicate whether thedetected scale signal is bad or good. As will be understood,additional/alternative categories could be available, such asacceptable, and/or optimal. Accordingly, the encoder module can beconfigured to determine and output the category the scale signal fallswithin. For example, in embodiments in which at least one parameter isdetermined via a process which analyses the quality of the detectedscale signal, the method can comprise determining which category theparameter falls within (e.g. via the use of predetermined thresholdvalues). Optionally, one or more visual output devices, such as a lightemitter, can be controlled so as to reflect the determined category(e.g. the colour of the light emitted could be dependent on thedetermined category).

As will be understood, the diagnostic information need not necessarilybe restricted to one of a plurality of predetermined categories. Rather,for example, in embodiments in which at least one parameter isdetermined via a process which analyses the quality of the detectedscale signal, the raw parameter determined can be output as thediagnostic information.

As mentioned above, the diagnostic information could be dependent on(and hence indicative of) the relative arrangement of the scale and thescale signal receiver, in particular in at least one dimension/degree offreedom other than that of the measuring dimension of the encodermodule. For example, the diagnostic information could be dependent on(and hence indicative of) any one, any combination, or all, of the scaleand scale signal receiver's lateral positon, ride-height, pitch, roll oryaw, with respect to each other. Accordingly, for example, thediagnostic information could be dependent on (and hence indicative of)when the scale and the scale signal receiver are, or are not, in adesired relative arrangement in at least one degree of freedom otherthan that of the measuring dimension. Such arrangement information canbe particularly useful for those embodiments which have a scale signalreceiver which is arranged independently of the scale, as described inmore detail below.

Optionally, the part of the encoder module that is moveable with respectto the scale can be configured to determine and output said diagnosticinformation. For example, optionally the readhead can be configured todetermine and output said diagnostic information. Accordingly,optionally the readhead could comprise said at least one processor.

Optionally, the encoder module is configured to output diagnosticinformation in the form of one or more human-detectable signals. Thesealed encoder module could comprise at least one output device foroutputting said diagnostic information as a human-detectable signal.Said output device can output a signal indicative of said diagnosticinformation. Said output device could comprise a visual output device.Said output device could be configured to emit an optical signal.Optionally, the least one output device is provided on said readhead.Optionally, said at least one output device is provided on saidprotective housing. As described in more detail below, the readheadcould comprise a mounting block external to said protective housing formounting the readhead to one of first and second moveable parts of amachine, and said output device can be provided on said mounting block.

Optionally, the encoder module is configured to output diagnosticinformation in the form of one or more electronic signals. For example,the encoder module could be configured to output diagnostic informationto an external device. Accordingly, the encoder module could comprise aninterface for transmitting said electronic signals, e.g. wirelessly, oralong a wire.

The scale signal could be the signal detected by one or more sensors(e.g. in the readhead) that are configured (and in use, used) to detectthe scale so as to determine said measure of the relative displacementof first and second parts of the machine (in the measuringdimension/degree of freedom). The scale signal could be the detectedsignal from the scale that is used to determine said measure of therelative displacement of first and second parts of the machine. Thescale signal could be an incremental scale signal. Accordingly, thediagnostic information could be determined from the output of anincremental signal sensor of the readhead. The incremental scale signalcould be an interference fringe. The scale signal could be a referencemark signal. Accordingly, the diagnostic information could be determinedfrom the output of a reference mark signal sensor of the readhead. Thescale signal could be an absolute scale signal. The scale signal couldbe an image of the scale (e.g. a one dimensional or two dimensionalimage of the scale). Accordingly, the diagnostic information could bedetermined from the output of an image sensor of the readhead. In otherwords, the diagnostic information could be determined from an image(e.g. a one or two dimensional image) of the scale.

Optionally, the scale signal used to determine diagnostic information isnot the signal that is used to determine said measure of the relativedisplacement. Optionally, the scale signal from which diagnosticinformation is determined is detected by at least one sensor other thanthe sensor(s) the output of which is(are) configured to be used todetermine said measure of the relative displacement of first and secondparts of the machine. Such a sensor could be referred to as a“diagnostic sensor”. Accordingly, in other words, the encoder modulecould be configured such that output of the diagnostic sensor is notused to determine said measure of the relative displacement of first andsecond parts of the machine.

As will be understood, the protective housing could be an integral partof a sealed encoder module. At least one of the scale and readhead canbe mounted to the protective housing. The sealed encoder module could beconfigured such that at least one of the scale and scale signal receiveris configured to be mounted to a part of a machine (the position ofwhich is to be measured by the sealed encoder module) via the protectivehousing. The housing could be configured to be mounted to a part of amachine. The protective housing could comprise one or more mountingfeatures via which the scale and/or scale signal receiver is configuredto be mounted to a part of a machine. Accordingly, optionally theprotective housing can lie between the scale and the part of the machinethat the encoder module is configured to be mounted to. Optionally, theprotective housing can lie between the scale signal receiver and thepart of the machine that the encoder module is configured to be mountedto.

A seal (e.g. at least one sealing lip) can be provided betweenrelatively moveable parts of the sealed encoder module. For example,between the protective housing and a relatively moveable readhead(described in more detail below). Optionally, the protective housingcomprises a plurality of (e.g. first and second) relatively moveableparts. Optionally, said plurality of (e.g. first and second) relativelymoveable parts of the housing are configured to be mounted to respectivedifferent parts of a machine, the relative position of which are to bemeasured by the sealed encoder module. A seal (e.g. at least one sealinglip) can be provided between the relatively moveable parts of theprotective housing. Optionally, the scale is mounted to a first part ofthe protective housing, and the readhead can be mounted to a second partof the protective housing.

Optionally, the scale or the scale signal receiver is mounted to firstpart (e.g. shaft part) of the protective housing which is configured tobe mounted to a shaft of the machine, and is configured to be rotatablewith respect to a second part of the protective housing to which theother of the scale and signal receiver is attached. Optionally at leastone compliant sealing ring is provided between the first and secondparts of the protective housing. Optionally, first and second compliantsealing rings are provided between the first and second parts of theprotective housing second. Said first and second compliant sealing ringscan be provided on opposite sides of the scale/scale signal receiver.

The scale signal receiver could be configured so as to be biased/bearagainst the scale and/or the part of the protective housing to which thescale is attached. Accordingly, the sealed encoder module could comprise“integral bearings” (and hence be what is known as an “integralbearing”, or “guided” encoder module). However, this need notnecessarily be the case. For example, the arrangement of the scalesignal receiver inside the protective housing could be independent ofthe scale and protective housing. Accordingly, the encoder module couldbe described as being “without integral bearing”, or as being a“bearingless” encoder module. Accordingly, as will be understood, thescale signal receiver could also be described as being “externallyconstrained” or as being “unguided”. Another way of looking at this isthat the scale signal receiver is held suspended (in other words in asuspended state) within the protective housing.

Optionally, the scale signal receiver and the protective housing aremoveable relative to each other along the measuring dimension of thescale. Optionally, the scale signal receiver can be located within (andprotected by) the protective housing, but not mounted to the protectivehousing. Optionally, a seal permits relative movement of the scalesignal receiver and the protective housing along the measuring dimensionof the scale. Accordingly, as described in more detail below, the sealcan extend along the measuring dimension. The seal could alsoaccommodate some relative movement of the scale signal receiver and theprotective housing in other dimensions.

Optionally, the arrangement of the scale and scale signal receiver (inat least one degree of freedom other than along the encoder's measuringdimension) is selectively adjustable. For example, optionally, at leastone of or any combination of the scale and scale signal receiver'slateral positon, ride-height, pitch, roll or yaw, with respect to eachother can be selectively adjusted. Accordingly, optionally, the encodermodule could comprise an adjustment mechanism for facilitating suchadjustment. Additionally, or alternatively, such adjustment can befacilitated by the features via which the scale and/or readhead aremounted to respective parts of a machine. For example, the features viawhich the scale and/or readhead are mounted to the respective parts of amachine could permit some flexibility in the positional relationship ofthe scale and scale signal receiver in said at least one degree offreedom. Such adjustability can be particularly useful in thoseembodiments in which the arrangement of the scale signal receiver insidethe protective housing is independent of the scale and protectivehousing (e.g. is “without integralbearing”/“unguided”/“bearingless”/“externally constrained”, etc).

Optionally, the scale signal receiver is located within (and protectedby) the protective housing, but not mounted to the protective housing.In this case, the protective housing can comprise a seal through whichthe scale signal receiver can be connected to a part outside theprotective housing. As will be understood, the part outside of theprotective housing to which the scale signal receiver can be configuredto be connected to, could be part of a machine, the position/movement ofwhich relative to another part of the machine (to which the scale issecured) is to be determined. The scale signal receiver can be connectedto a part of a machine located outside the protective housing, via amount member. In those embodiments in which the arrangement of the scalesignal receiver inside the protective housing is independent of thescale and protective housing, the scale signal receiver can be rigidlyconnected to a part of the machine located outside the protectivehousing. Accordingly, the mount member could be a rigid mount member.Accordingly, said rigid connection/rigid mount member can be configuredsuch that the position and orientation of the scale signal receiverwithin the protective housing, in all six degrees of freedom, can bedictated by (and mastered to) the part outside the protective housing towhich the scale signal receiver is configured to be attached to. Forexample, in embodiments in which the readhead comprises mountingfeatures (described below), the position and orientation of the scalesignal receiver within the protective housing, in all six degrees offreedom, can be dictated by (and mastered to) the mounting features(e.g. dictated by/mastered to a mounting block on which said mountingfeatures are provided). For example, the scale signal receiver can berigidly fixed to a rigid readhead mount member which passes through theseal. Accordingly, the position and orientation of the scale signalreceiver on the first side of the seal (inside the protective housing)can be dictated by (and mastered to) the readhead mount.

Optionally, the protective housing comprises at least one (for exampleelongate, optionally linear) compliant sealing member through which thescale signal receiver can be mounted to a part of the machine.

Said mount could be provided by the part of the machine to which thescale signal receiver is to be attached. For example, the machine itselfcould comprise a (rigid) mounting bracket that is inserted into theprotective housing and connected to the scale signal receiver.Optionally, the readhead can comprise a readhead mount comprising one ormore mounting features located outside the protective housing forsecuring the readhead to a part of a machine. As will be understood, thereadhead could be configured to be releasably fastened to a part of amachine. The one or more mounting features could be provided on amounting block. A mounting feature could comprise, for example, a holeinto and/or through which a releasable fastener (e.g. a bolt) can pass(and optionally engage). As will be understood, the scale signalreceiver of the readhead can be rigidly connected to the readhead mount(which as explained above can be rigid so as to ensure a rigidconnection between the scale signal receiver and a part outside theprotective housing). As will be understood, the scale signal receiver,readhead mount and blade could be formed as a single monolithicstructure, or could comprise a plurality of separately formed units,rigidly connected to each other.

The mount could comprise a (e.g. rigid) blade-like member configured toextend through the seal. In those embodiments in which the readheadcomprises the readhead mount as described above, the blade-like membercould extend through the seal between the scale signal receiver that islocated inside the protective housing and the mounting features that islocated outside the protective housing. The blade-like member couldcomprise first and second edges (in other words, leading and trailingedges). The blade-like member could be tapered towards the first andsecond edges. The blade-like member could comprise an internalpassageway/channel for wires and/or air to pass through between theinside and outside of the protective housing, for example between thescale signal receiver and a mounting block on which the one or moremounting features are provided.

The protective housing can comprise one or more mounting features formounting the protective housing to a part of a machine (e.g. todifferent part of the machine to which the scale signal receiver isconfigured to be mounted to, said parts of the machine being relativelymovable with respect to each other). Said one or more mounting featurescould be configured to facilitate releasable mounting of the protectivehousing. A mounting feature can comprise a hole into and/or throughwhich a releasable fastener (e.g. a bolt) can extend (and optionallyengage).

As will be understood, the scale signal receiver can be the part of thereadhead located inside the protective housing which receives the signalfrom the scale. The scale signal receiver can comprise one or morecomponents for interacting with the scale signal, e.g. so as to detectthe scale signal and/or manipulate the scale signal before it issubsequently detected. For example, in the case of an optical encoder,the scale signal receiver can comprise one or more optical elements,such as diffractive and/or refractive optical elements. For example, thescale signal receiver can comprise one or more lenses, and/or one ormore diffraction gratings. The scale signal receiver could comprise oneor more signal guides for guiding the scale signal to another component.For example, in the case of an optical encoder, the scale signalreceiver could comprise a wave guide, e.g. a light guide (for instance,an optical fibre). The signal guide could be configured to carry thescale signal to a subsequent component which interacts with the scalesignal, e.g. so as to manipulate the scale signal. The signal guidecould be configured to carry the scale signal to one or moredetector(s)/sensor(s) configured to detect the scale signal, e.g. atransducer.

Optionally, the readhead comprises one or more sensors for sensing thescale signal (which as described above may or may not have beenmanipulated by one or more components in the readhead). A sensor couldcomprise a plurality of sensor elements, e.g. an array of sensorelements. The scale signal receiver could comprise the sensor(s).Optionally, the sensor(s) could be located elsewhere in the readhead.For example, the sensor could be located in a part of the readhead whichis located outside the protective housing. For example, in thoseembodiments in which the readhead comprises a mounting block (describedin more detail below), the sensor(s) (and indeed any other componentsmentioned above) could be located in the mounting block.

In those embodiments in which the scale signal receiver comprises anouter casing (described in more detail below), the scale signal receivercan comprise one or more features for enabling the signal from the scaleto enter the scale signal receiver. For example, in the case of anoptical encoder, the scale signal receiver could comprise a window.

The readhead can comprise one or more emitters for emitting energytoward the scale. For example, the readhead can comprise at least onelight source configured to illuminate the scale (e.g. with light in theinfra-red to ultraviolet range). The scale signal receiver can comprisesaid one or more emitters. Optionally, said one or more emitters can beprovided by another part of the readhead (e.g. outside the protectivehousing, such as by a mounting block).

Optionally, the readhead, e.g. the scale signal receiver, (for instanceits sensor(s)) is configured to detect a signal generated by lightcoming from the scale. Optionally the light has been transmitted throughthe scale. Optionally, the light has been reflected from the scale.Accordingly, optionally, the readhead, e.g. the scale signal receiver,comprises an emitter (e.g. a light source) and a sensor. The emitter andsensor could be located on the same side of the scale. Accordingly, theencoder can be a reflective encoder apparatus.

As will be understood, the scale will have some form offeatures/markings which can be read by the readhead to determinedisplacement, position (or its derivatives, e.g. velocity and/oracceleration). Such features could define a pattern. For example, anincremental scale could comprise scale features/marks that define aperiodic pattern and which can be used to generate a periodic signal atthe readhead (e.g. when relative movement between the scale and thereadhead takes place). The scale can be elongate. The scale can comprisea substrate in and/or on which the features/markings are formed.

Optionally, the encoder apparatus is a diffraction-based encoderapparatus. Optionally, the scale comprises features configured todiffract light (in the ultraviolet to infra-red range) which is used toform a resultant signal on a sensor in the readhead. Optionally, thereadhead comprises one or more optical elements configured to interactwith light before and/or after the scale in order to form the signal ona sensor in the readhead assembly. Optionally, the readhead comprisesone or more lenses and/or one or more diffraction gratings. Optionally,the readhead comprises a diffraction grating configured to interact withlight from scale the scale to form an interference fringe on a sensor inthe readhead. Optionally, the sensor comprises an electrogratingcomprising two or more sets of interdigitated sensors, each set beingconfigured to detect a different phase of an interference fringe.

Optionally, the scale comprises absolute scale features which define a(e.g. continuous) series of uniquely identifiable positions along thelength of the scale.

Optionally, the readhead is configured to detect an image of the scale.Optionally, the readhead (e.g. the scale signal receiver) comprises atleast one imaging optical element configured to form an image of thescale onto a sensor. Optionally, the readhead comprises at least onesensor suitable for capturing an image, e.g. at least Charge-CoupledDevice (CCD) or Complementary Metal-Oxide-Semiconductor (CMOS) sensor.

As will be understood, references in this application to optical andreferences to light are intended to refer to electromagnetic radiation(EMR) in the ultraviolet to infra-red range (inclusive).

As will be understood, the readhead can be configured to determine andoutput information concerning the relative position of the scale signalreceiver and the scale (referred to herein as “position information”).Optionally, the readhead comprises one or more processor devicesconfigured to process the output from one or more detector(s)/sensor(s),e.g. so as to form said position information. The position signal can beincremental position information. For example, the position signal cancomprise a quadrature signal. Optionally, the position signal comprisesabsolute position information. Said one or more processor devices couldbe located in the scale signal receiver and/or in another part of thereadhead assembly (e.g. in the readhead mount).

The encoder apparatus could comprise a magnetic, inductive, capacitive,and/or optical encoder apparatus. Accordingly, the scale could comprisemagnetic, inductive, capacitive, and/or optical scale. Optionally, theencoder apparatus comprises an optical encoder apparatus.

The scale can comprise rotary scale. The rotary scale can comprise whatis commonly referred to as disc scale (in which the scale features areprovided on the face of the disc). The rotary scale can comprise what iscommonly referred to as ring scale (in which the scale features areprovided on the circumferential edge of the disc). Optionally, the scaleis arc-shaped. Optionally, the scale can comprise linear scale.

Optionally, the encoder module has a nominal ride-height of not lessthan 0.1 mm, for example not less than 0.2 mm, for instance not lessthan 0.5 mm. Optionally, the encoder apparatus has a nominal ride-heightof not more than 5 mm, for example not more than 2 mm, for instance notmore than 1 mm. Optionally, the allowable ride-height variation(“tolerance”) for the encoder module is not less than +/−50 μm(microns), optionally not less than +/−75 μm (microns), for example atleast +/−100 μm (microns).

The protective housing can be elongate. The protective housing can besubstantially straight. The protective housing can comprise asubstantially tubular form. The cross-sectional shape of said tubularprotective housing need not necessarily be round, but for example couldcomprise other regular or irregular shapes. For example, thecross-section shape of said tubular protective housing could besubstantially rectangular. Optionally, the protective housing is round,for example circular, for instance ring-shaped.

Said seal can extend along the encoder apparatus' measurement dimension.Optionally, the seal is provided by a flow of gas, e.g. across a gap inthe protective housing, and/or for example via a positive (e.g. air)pressure inside said protective housing. Optionally, the seal comprisesa physical barrier. The seal could comprise a plurality, for example apair, of seal members. For example, the seal could comprise a plurality(e.g. a pair) of sealing lips (e.g. which could be elongate orannular/ring-shaped). In those embodiments in which the scale signalreceiver can be configured to be connected to a part of a machinelocated outside the protective housing via a mount member, the mountmember could pass through the seal, e.g. between the sealing lips. Forexample, the above mentioned blade-like member could pass through theseal, e.g. between the sealing lips.

Optionally, the seal (e.g. the sealing lips) is (are) compliant.Optionally, the seal (e.g. the sealing lips) is (are) elastic. Forexample, the seal (e.g. the sealing lips) is (are) sufficientlycompliant so as to enable the relative movement of the relativelymoveable parts of the encoder module. For example, the seal could permitrelative movement of the scale/protective housing and the scale signalreceiver, for instance by permitting the member, e.g. blade-like member,and the protective housing/seal to move relative to each other.Optionally, the seal (e.g. the sealing lips) is (are) biased toward asealed configuration, e.g. by way of their elasticity. The seal (e.g.the sealing lips) could comprise, for example, polyurethane, such asthermoplastic polyurethane, and/or fluorinated elastomer.

The readhead can comprise at least one vibration control device. Such adevice can be particularly beneficial for those embodiments in which thescale signal receiver is arranged independently of the scale (e.g. whichis “externally constrained”), described in more detail below. As will beunderstood, such a vibration control device can be configured to reducethe susceptibility of the readhead (e.g. of the scale signal receiver)to vibrations. A vibration control device can be a device configured toreduce the response of at least part of a system (e.g. the scale signalreceiver of the readhead) due to external excitation. The vibrationcontrol device can comprise at least one member which is configured tovibrate independently of the readhead, e.g. independently of the scalesignal receiver. The vibration control device can comprise at least onemember which is configured with a resonant frequency independent of theparts of the readhead assembly that are located inside the protectivehousing (e.g. of the scale signal receiver). Optionally, the vibrationcontrol device comprises at least one member which is configured with aresonant frequency different that of the parts of the readhead that arelocated inside the protective housing (e.g. different to that of thescale signal receiver).

The vibration control device can comprise a tuned mass damper. The tunedmass damper can be tuned so as to reduce the amplitude of vibrations inat least the part of the readhead assembly (e.g. of at least the scalesignal receiver) in which it is installed, at and around that part'sresonant frequency. A tuned mass damper can comprise at least one springelement. A tuned mass damper can comprise at least one damper element. Atuned mass damper can comprise at least one mass element. The at leastone spring's stiffness “k”, the at least one damper's dampingcoefficient “c” and the at least one mass's mass “m” can be selected (inother words “tuned”) so as to reduce the amplitude of vibrations of atleast the part of the readhead assembly (e.g. of at least the scalesignal receiver) in which it is installed, at and around that part'sresonant frequency.

The scale signal receiver can comprise an outer case. The outer case,can be configured to protect components of the scale signal receiverthat are located inside the protective housing from contamination (e.g.solid or fluid such as swarf or coolant, or for example moisture) thatdoes happen to enter the protective housing. In particular, the outercase can be configured to provide protection against fluid, for example,liquid. Said outer case could encapsulate said components. Saidcomponents can comprise electrical components, including any wiresand/or any printed circuit boards. Said components can comprise theabove described components which are configured to interact with thescale signal. The outer case can be a sealed body, for example ahermetically sealed case.

Accordingly, the sensor componentry of the scale signal receiver can becontained within a sealed body/outer case. In other words, the scalesignal receiver's electrical and/or other componentry used, for examplein the detection of the scale signal, can be contained within a sealedbody/outer case. For example, in the case of an optical encoderapparatus, optical components such as a lens, diffraction grating,beam-steering device or beam-divider can be contained with the sealedbody/outer case. The readhead's emitter (e.g. a light emitter) can becontained within the sealed body/outer case. A window (e.g. sealedwindow) in the sealed body/outer case can be provided for permitting thescale signal to enter the sealed body/outer case.

Further optional features of the outer case are explained below inconnection with the second aspect of the invention, which are notrepeated here for conciseness, but which are equally applicable to thisfirst aspect and other aspects of the invention, and vice versa.

According to a second aspect of the invention there is provided a sealedencoder module for mounting onto a machine so as to measure relativedisplacement of first and second parts of the machine, the sealedencoder module comprising, a scale, a readhead comprising a scale signalreceiver, and a protective housing which encapsulates at least the scaleand said scale signal receiver, in which the scale signal receivercomprises an outer case within which one or more components of thereadhead are contained.

Providing the scale signal receiver with an outer case can help toensure that one or more components of the scale signal receiver (i.e.component(s) for effecting the detection of the scale signal, e.g.electronic components and/or other components used for generating and/orinteracting with, such as sensing and/or manipulating, the signal fromthe scale) is/are protected even if contamination does manage to getinside the protective housing. In particular, the outer case can beconfigured to provide protection against fluid, for example, liquid.This can improve the reliability and longevity of the encoder apparatus.Such a component can comprise an electronic component, including anywires and/or any printed circuit boards. Such a component can comprise asensor. Such a component can comprise a component which interacts withthe scale signal (e.g. used to manipulate the signal from the scalebefore it is sensed by the readhead's sensor). Such a component cancomprise an emitter, such as a light emitter, e.g. for illuminating thescale. In the case that the encoder apparatus comprises an opticalencoder apparatus, the scale signal receiver's optical component(s) canalso be located inside said outer case.

The outer case can be a rigid case. Such a rigid case can be configuredto protect the one or more components, (including any wires and/or anyprinted circuit boards) against solid objects which enter the protectivehousing. The outer case could be substantially box-like. For example, itcould have a generally rectangular cross-sectional profile. The outercase can provide a void/internal volume within which the one or morecomponents of the scale signal receiver are located. The outer case canprovide the structure (e.g. load bearing structure) to which one or morecomponents of the scale signal receiver are mounted. The outer case canbe (can be configured to be) mounted to one of the first and secondparts of the machine. This could be via the protective housing. Thiscould be via a readhead mount, e.g. as described above in connectionwith the other aspects of the invention. For example, the outer casecould be mounted to one of the first and second parts of the machine viaa mounting block. In embodiments in which the protective housingcomprises a seal through which the scale signal receiver can beconnected to a part outside the protective housing, the outer case cancomprise the part which extends through the seal. For example, inembodiments in which there is a blade-like member (as described above),the blade-like member can be part of the outer case. In particular, theblade-like member can contain and protect wires or otherelectrical/optical components from contamination which enters theprotective housing.

As will be understood, the outer case can comprise a plurality ofcomponents, e.g. a body and a lid, which together define an internalvolume within which the one or more components of the readhead arecontained.

The outer case can encapsulate at least all of the electroniccomponents, including any wires and any printed circuit boards, of thescale signal receiver which are located within the protective housing.In the case of an optical encoder, the outer case could encapsulate allof the optical components used in the detection of the scale signal(e.g. any combination of one or more lenses, diffraction gratings, beamsplitters, light sources, and beam steerers), except for an outer-sideof one or more windows through which the scale signal enters the casingand/or through which light from a light emitter exits the outer casetoward the scale. Accordingly, as will be understood, any such windowscan form part of the outer case. Optionally, any electronic componentthat comprises a protective shell or body (e.g. which shields the bareelectronics of the electronic component) can itself form part of theouter case.

The encoder apparatus could comprise a reflective optical encoderapparatus. In such embodiments the light source for illuminating thescale and the detector for detecting the scale can be located on thesame side of the scale. In such embodiments, the same (e.g. a single)outer case can comprise the light source and the detector.

Preferably the outer case provides solid particle protection to at leastlevel 4, and liquid ingress protection to at least level 4, according tothe International Protection Marking (also known an Ingress ProtectionMarking), International Electrotechnical Commission (IEC) standard60529. In other words, preferably the outer case has an IP rating of atleast IP44. The outer case could provide solid particle protection to atleast level 5, optionally to at least level 6. The outer case couldprovide liquid ingress protection to at least level 5, optionally to atleast level 6, for instance to at least level 7. In other words, theouter case could have an IP rating of IPxy where x (which relates tosolid particle protection) is at least 4 (e.g. 4 to 6) and y (whichrelates to liquid ingress protection) is at least 4 (e.g. 4 to 7). Aswill be understood, features explained above and below in connectionwith the other aspects of the invention are equally applicable to thisaspect of the invention, and vice versa.

According to a third aspect of the invention there is provided anencoder apparatus comprising a scale and a readhead assembly moveablerelative to each other, the readhead assembly comprising a scale signalreceiver, the scale and the scale signal receiver being located within aprotective housing which is configured to protect them fromcontamination located outside the protective housing and comprises aseal through which the scale signal receiver can be connected to a partoutside the protective housing, in which the arrangement of the scalesignal receiver inside the protective housing is independent of thescale and protective housing. As will be understood, features explainedabove and below in connection with the other aspects of the inventionare equally applicable to this aspect of the invention, and vice versa.

According to a fourth aspect of the invention there is provided areadhead assembly for an encoder apparatus (e.g. comprising at least onesensor for sensing scale features) comprising at least one vibrationcontrol device configured to reduce the susceptibility of at least apart of the readhead assembly (e.g. a scale signal receiving part) tovibrations. Accordingly, this application describes a readhead for anencoder apparatus comprising at least one sensor for sensing scalefeatures and at least one vibration control device configured to vibrateindependently of the rest of the readhead. Providing a readhead with atleast one vibration control device can control vibrations transferredthrough to it from the machine on which it is mounted. This isparticularly useful where the readhead is mounted to the machine via astructure that is susceptible to vibration (e.g. via an elongatemember). As will be understood, features explained above and below inconnection with the other aspect of the invention are equally applicableto this aspect of the invention, and vice versa. Accordingly, forexample, the readhead could comprise a scale signal receiver. The scalesignal receiver could comprise the at least one vibration controldevice. In those embodiments in which the scale signal receiver ismounted via an elongate blade, the scale signal receiver and/or elongateblade could comprise at least one vibration control device.

According to a fifth aspect of the invention there is provided a machinecomprising an encoder apparatus and/or readhead as described above.

According to another aspect of the invention there is provided a methodof setting up a sealed encoder module for measuring the relativeposition of two relatively moveable parts of a machine in a first degreeof freedom, the sealed encoder module comprising, a scale, a readheadcomprising a scale signal receiver, and an integral protective housingwhich encapsulates at least the scale and said scale signal receiver,wherein the sealed encoder module is configured to determine and outputdiagnostic information, the method comprising using said diagnosticinformation to determine whether the scale and the scale signal receiverare in a desired relative positional relationship in at least one degreeof freedom other than the first degree of freedom. The method cancomprise an operator adjusting the relative position of the scale andthe scale signal receiver in response to an indication that the scaleand the scale signal receiver are not in a desired relative positionalrelationship in at least one degree of freedom other than the firstdegree of freedom. In accordance with the above and below descriptions,the diagnostic information could be presented to an operator via a lightemitter. Accordingly, the method can comprise the operator adjusting therelative position of the scale and the scale signal receiver in responseto the output of the light emitter, e.g. in response to the colour ofthe light emitted by the light emitter.

Embodiments of the invention will be described, by way of example only,with reference to the accompanying drawings in which:

FIG. 1a schematically illustrates a sealed encoder according an aspectof the invention;

FIG. 1b schematically illustrates the sealed encoder of FIG. 1a withpart of the protective housing cut-away to show the scale and scalesensor assembly located inside the protective housing;

FIG. 1c is a cross-section through the sealed encoder apparatus of FIG.1 a;

FIG. 1d schematically illustrates the sealed encoder of FIG. 1a withpart of the protective housing cut-away to show the scale and scalesensor assembly located inside the protective housing;

FIGS. 2a and 2b are schematic illustrations of another embodiment of asealed encoder apparatus according an aspect of the present invention,with part of the protective housing cut-away to show the scale and scalesignal receiver located inside the protective housing;

FIG. 2c is a cross-section through the sealed encoder apparatus of FIGS.2a and 2 b;

FIG. 2d is a cross-section through an alternative embodiment of a sealedencoder apparatus;

FIG. 3 is an illustration of another alternative embodiment of areadhead assembly suitable for use with a sealed encoder, with part ofthe signal receiving module cut-away to expose its internal components;

FIG. 4 is an illustration of the signal receiving module of the sealedencoder apparatus of FIG. 3;

FIG. 5 is an illustration of a tuned mass damper used in the signalreceiving module of FIGS. 3 and 4;

FIGS. 6a and 6b illustrate an alternative way of implementing avibration control device on a readhead assembly;

FIGS. 7a and 7b illustrate yet another way of implementing a vibrationcontrol device on a readhead assembly;

FIGS. 8a to 8c schematically illustrate further ways of implementing avibration control device;

FIGS. 9a and 9b schematically illustrate rotary embodiments of theinvention; and

FIGS. 10a and 10b illustrate an alternative embodiment of a rotaryencoder implementing according to the invention.

Referring initially to FIGS. 2a to 2d there is a sealed encoder module102 according to the invention. The sealed encoder module 102 comprisesa scale 104 having a plurality of features (not shown) and a readheadassembly 103, comprising a scale signal receiver 106 for receiving asignal from the scale. In the embodiment described the sealed encodermodule 102 is an optical encoder, in that the readhead assembly 103utilises electromagnetic radiation (EMR) in the infra-red to ultravioletrange in order to read the scale 104. In particular, in this describedembodiment, the position measurement encoder apparatus is an opticalabsolute encoder. Accordingly, the scale comprises a series of uniquelyidentifiable features, e.g. codes, which the readhead assembly 103 canread and process to determine a unique position along the length of thescale 104. However, as will be understood, the position measurementencoder apparatus need not necessarily be an absolute encoder. Forexample, it could be an incremental optical encoder. Furthermore, theencoder apparatus need not be an optical encoder, for example, theencoder apparatus could be a magnetic encoder, or for instance aninductive encoder.

The readhead assembly 103 communicates with an external processor device(not shown), e.g. a controller, via a communications channel which inthe described embodiment comprises a physical connection (e.g. cable105) as opposed to a wireless connection. The communication channel canbe two-way such that the readhead assembly 103 can receive data (e.g.instructions) from the external processor device as well as send data(e.g. position information/signals) to the external processor device.Power to the readhead assembly 103 can also be supplied via a physicalconnection, e.g. via the cable 105. However, this need not necessarilybe the case. For example, the readhead assembly 103 could comprise aninternal power source such as a battery.

The scale 104 and scale signal receiver 106 are located inside aprotective housing 108 which protects them from contaminants external tothe protective housing. The scale 104 is fixed to the protective housing108 whereas the scale signal receiver 106 can move along the length ofthe scale 104 within the protective housing 108. In use, the protectivehousing 108 will be secured to a first part of a machine (not shown) andthe scale signal receiver 106 will be secured to a second part of themachine (not shown). As will be understood, the first and second partsof the machine are relatively moveable with respect to each other. Thereadhead assembly further comprises a mounting block 114 which is to bedirectly fastened to the second part of the machine (e.g. via one ormore releasable fasteners, such as threaded bolts passing through holes115), and a blade 116 which is connected to and extends between themounting block 114 and the scale signal receiver 106. A light source 113is provided on one end of the mounting block 114 and is used (asexplained in more detail below in connection with the other embodimentsof the invention) to relay diagnostic information concerning the encoderto an operator/installer.

The protective housing 108 further comprises a seal 111 in the form of apair of sealing lips 112 which seals the inside of the protectivehousing 108, in which the scale 104 and scale signal receiver 106reside, from external contaminants. The blade 116 passes between thepair of sealing lips 112. The sealing lips 112 are compliant so as to beable to part so as to allow the movement of the blade 116 and hence thescale signal receiver 106 along the length of the protective housing 108and hence the scale 104, but are also sufficiently elastic so as toclose together around the blade 116, thereby forming a physical barrierto solid and fluid (in particular liquid and moisture) contaminants. Inother words, the blade 116 prises the sealing lips 112 apart as it movesalong the length of the seal, between the sealing lips 112, and thesealing lips have sufficient elasticity so as to close together in theabsence of the blade 116,

The arrangement of the scale signal receiver 106 within the protectivehousing is independent of the scale 104 or the protective housing 108.It is rigidly connected to the mounting block 114. In particular, thescale signal receiver 106 is rigidly connected to the blade 116, whichin turn is rigidly connected to the mounting block 114. Accordingly, theposition of the scale signal receiver 106 in all degrees of freedom isdictated by the position of the mounting block 114 and hence dictated bythe position of the second part of the machine to which the mountingblock 114 is secured during use, and not by the scale 104 or other partinside the protective housing 108.

In the embodiment described the scale signal receiver's 106 position andmotion is not constrained or guided in any way by the scale 104 orprotective housing 108. Due to the rigid mount between the scale signalreceiver 106 and the mounting block 114 the position and motion of thescale signal receiver 106 in all six degrees of freedom is constrainedand guided by the position and motion of the mounting block 114, andhence the part of the machine to which the mounting block 114 issecured. Accordingly, the position and motion of the scale signalreceiver 106 could be described as being “externally constrained”. Also,the scale signal receiver 106 does not bear against the scale 104.Accordingly, such a sealed encoder could be described as being “withoutintegral bearing”, or “bearingless”. We consider that this is a novelarrangement for a sealed encoder (and is the subject of a co-pending PCTpatent application titled “Encoder Apparatus” having the same prioritydate and priority claim as the present application), and is in contrast,for example, to the known configuration of a sealed “integral bearing”linear encoder which biases/bears the scale signal receiver against thescale and provides a compliant coupling between the scale signalreceiver and its mounting block. An example of such an “integralbearing” arrangement is described below in connection with theembodiment shown in FIGS. 1a to 1d . Such an arrangement could bedescribed as being “internally constrained”.

As will be understood, if desired, an adjustment mechanism could beprovided for adjusting the relative set-up position of the scale signalreceiver 106 with respect to the mounting block 114 (e.g. the scalesignal receiver could be connected to the blade 116, and/or the blade116 could be mounted to the mounting block 114, via a joint whichfacilitates selective adjustment of their relative position in at leastone linear and/or one rotational degree of freedom, for example bymanipulation of a micro/grub screw). Such a selective adjustmentmechanism could be useful to aid set-up/alignment of the encoderapparatus. However, as will be understood, such a selective adjustmentmechanism will still provide a rigid connection between the scale signalreceiver 106 and the readhead mount 114, and hence a rigid connectionbetween the scale signal receiver 106 and the part of the machine onwhich it is mounted (i.e. so that during use/operation, theposition/orientation of the scale signal receiver 106 in all degrees offreedom is still mastered to/dictated by the second part of the machineto which the mounting block 114 is mounted).

In the described embodiment, the scale signal receiver 106 does notcontact the scale 104, nor the protective housing 108 at all.Accordingly, there is a gap all the way around the scale signal receiver106, between it and the scale 104 and the inside of protective housing108. Indeed, as shown, in the embodiment described, the only contactbetween the readhead assembly 103 (which comprises the scale signalreceiver 106 and the readhead mount 110) and the protective housing 108is between the blade 116 and the pair of sealing lips 112. As will beunderstood, the pair of sealing lips 112 are flexible and elastic inbehaviour and yield to accommodate the blade 116, and thereby do notconstrain or control the position of the scale signal receiver 106.

Furthermore, in the embodiment described, the scale signal receiver 106comprises an outer case 107, inside of which is located the scale signalreceiver's electrical components. The scale signal receiver's 106 sensorfor detecting the scale signal coming from the scale 104, and also anyassociated components for forming the scale signal on the sensor (e.g.optical components such as a lens, diffraction grating and/or mirrors)can also be provided inside the scale signal receiver's outer case 107.The outer case 107, is configured (e.g. sealed) such that ifcontamination did inadvertently pass through the lip seals 112, then thescale signal receiver's 106 components (in particular the electrical andoptical components) inside the outer case 107 are protected.

As will be understood, in embodiments in which an outer case 107 isprovided, a window (e.g. window 232 in FIGS. 3 and 4) can be provided toenable the scale signal to reach the sensor located inside the outercase 107. Optionally, the window has no material effect on the scalesignal (e.g. its only purpose could be to merely allow the signal fromthe scale to enter the outer case 107 without contributing to the formof the signal received at the readhead's sensor). Optionally, the windowcould be configured to re-direct the signal coming from the scale (e.g.it could comprise a mirror). Optionally, the window could be configuredto interact with the signal from the scale so as to produce the desiredsignal detected at the sensor. For example, it could comprise adiffraction grating, and/or lens. In any case, as will be understood,the outside of the window 232 will not be sealed from any contaminationentering the protective housing 108, since it forms part of the outercase 107, but the inside of the window, and any other components (e.g.optical components) which are configured to manipulate the signal comingfrom the scale 104 are protected from contamination.

The benefits of providing the scale signal receiver 106 with an outercase 107 can be beneficial not just for embodiments in which the scalesignal receiver 106 is independently arranged with respect to the scale(e.g. is “bearingless” or “externally constrained”), but can also bebeneficial for embodiments in which the scale signal receiver is biasedagainst the scale (comprises “integral bearings”), e.g. is mounted tothe readhead mount via an articulated linkage and the position of whichis “internally constrained” (e.g. can also be beneficial in enclosedencoders of the type described below in connection with FIGS. 1a to 1d). Accordingly, as will be understood, in connection with this aspect,there could be provided an articulated linkage such as that described inconnection with FIGS. 1a to 1d . However, although providing an outercase 107 can improve the resilience of an enclosed encoder with“integral bearings” (e.g. of an encoder with an “internally constrained”scale signal receiver), if contamination does pass through the sealinglips 12 and lands on the scale, this can adversely affect theperformance of the encoder apparatus. For example, if sufficientcontamination landed on the scale features then this could adverselyaffect the signal coming from the scale. Also, if solid contaminationsuch as swarf entered the protective housing and fell on the track(s)along which the readhead's bearings 20 run, this could adversely affectthe relative position/orientation of the scale signal receiver and scaleas the scale signal receiver rides over the dirt. Of course, an enclosedencoder with a scale signal receiver arranged independently of the scale(e.g. “externally constrained”) has the additional benefit of notsuffering from such a problem.

As explained in more detail below in connection with the otherembodiments of the invention, the scale signal receiver 106 receives asignal from the scale which is processed in order to provide, via cable105 for example, a position signal to an external device (such as amachine controller). For example, processing to determine the positioncould be performed by one or more processor devices in the scale signalreceiver 106, and/or by one or more processor devices in another part ofthe readhead assembly such as the mounting block 114. Optionally, theblade 116 comprises one or more channels to enable wires to pass betweenthe scale signal receiver 106 and the mounting block 114. Alternatively,wireless communication could be used, or wired connections external tothe blade 116 could be used. If the blade 116 comprises one or morechannels, then air (for example supplied via an air supply line 109)could be passed through to the inside of the protective housing 108 viathe blade 116 (e.g. via holes in the blade 116) scale signal receiver.

As will be understood, FIGS. 2a to 2d are schematic and typically theseparation between the scale 104 and scale signal receiver 106 (oftenreferred to as the ride-height) can be much smaller than that shown. Thedesired ride-height will depend on the encoder, but for example, typicalride-heights for optical encoders can be in the region of 0.24 mm to 2mm. In the particular example described, the nominal ride-height is 0.8mm, with a +/−0.15 mm tolerance.

The sealed encoder module 102 shown in FIGS. 2a to 2d can be used in anyorientation. In FIGS. 2a to 2d , the mounting block 114 is shown to bepositioned directly above the scale signal receiver 106 and theprotective housing 108. However, this need not necessarily be the case.For example, the sealed encoder module 102 could be mounted on its side,or even upside down (such that the mounting block 114 is positioneddirectly below the scale signal receiver 106 and the protective housing108). Indeed, such an arrangement can be advantageous because anyexternal contamination will tend to fall away from the lip seals 112 ofthe protective housing 108 due to gravity.

Likewise, the pair of sealing lips 112 need not be provided directly onthe side of the protective housing 108 that is opposite the side of theprotective housing 108 on which the scale is located. For example, withreference to the orientation shown in FIG. 2c , the sealing lips 112could be provided on one of the vertical sides of the protective housingsuch that the blade 116 extends horizontally as opposed to vertically.Alternatively, they could be provided along one of the corners/edges ofthe protective housing between two sides, such as shown in FIG. 2d(which as shown in this embodiment the seal 111 comprises two pairs ofsealing lips 112).

Referring now to FIGS. 3 to 5, there is shown another readhead assembly203. The readhead assembly 203 of FIGS. 3 to 5 shares many similaritieswith the readhead assembly 103 of FIG. 2 and for instance comprises ascale signal receiver 206, a mounting block 214, a light emitter 213,and a blade 216 providing a rigid connection between the scale signalreceiver 206 and the mounting block 214 (accordingly, the scale signalreceiver 206 is “externally constrained”). FIG. 3 shows the readheadassembly 203 in isolation, but as will be understood the readheadassembly 203 is intended to be used to read a scale that is locatedinside a protective housing, like that shown in FIGS. 2a to 2d .Accordingly, it is also intended that the scale signal receiver 206 willalso be located inside the protective housing, and the blade 216 willpass through an elongate seal in the protective housing, such as a pairof sealing lips. As with the embodiment of FIGS. 2a to 2d , the scalesignal receiver 206 is an optical readhead, but this need notnecessarily be the case.

As with the scale signal receiver 106 of FIG. 2, the scale signalreceiver 206 of FIGS. 3 and 4 comprises a protective outer case 207. Inthis case, the components inside the scale signal receiver 206 areprotected (e.g. sealed) by way of the protective outer case 207 and amounting face 217 provided at the end of the blade 216 proximal thescale signal receiver 206 via which the scale signal receiver 206 ismounted to the blade 216. A sealing member can be provided at theinterface between the outer case 207 and the mounting face 217 (e.g. agasket could be sandwiched between the outer case 207 and the mountingface 217 of the blade 216).

As shown, rather than the blade 216 extending perpendicularly betweenthe scale signal receiver 206 and the mounting block 214 (as in theconfiguration of FIG. 2), in this embodiment the blade extends at anon-perpendicular angle, for example approximately 45 degrees betweenthe scale signal receiver 206 and the mounting block 214. This is suchthat the blade can be oriented such that any liquid falling on it willfall away from the sealing lips, regardless of whether the sealedencoder module is mounted vertically or horizontally.

As shown in FIGS. 3 and 4 there is shown an optical unit 230 comprisingthe scale signal receiver's components for detecting the scale signal.In particular, the optical unit comprises a light source 252 forilluminating the scale, a lens 254 configured to image the scale, asensor 256 on which said image falls and is configured to detect saidimage (e.g. a one or two dimensional CCD or CMOS sensor), and a beamsteerer 258 which is configured to direct light from the light sourceonto the scale. As shown, the sensor 256 can be mounted on a printedcircuit board (PCB) 240. A cable (not shown) connects the PCB 240 to aprocessor device inside the mounting block 214. When an image isobtained by the sensor, it is passed to the processor device locatedinside the mounting block 214, which processes the image to determine aposition (in a known manner, e.g. as explained in US2012/072169, thecontent of which is incorporated herein by this reference). Thedetermined position is then communicated to an external device (such asa machine controller for example), for example via one or more signalstransmitted along cable 205. As will be understood, other arrangementsare possible. For example, all processing could be performed by one ormore processor devices located in the scale signal receiver 206. Inanother alternative embodiment, the sensor device (e.g. a CCD or CMOS)could be located in the mounting block and could receive the scalesignal via a light guide (e.g. fibre optic) that extends through theblade 216. Accordingly, in this case the scale signal receiver 206merely collects the signal/light from the scale and passes it through toa sensor located elsewhere in the readhead assembly.

As mentioned above, a light emitter 213 (113 in the embodiment of FIGS.2a to 2d ) for relaying diagnostic information can be provided by theencoder module; for example by the readhead assembly. Such a lightemitter can be used to relay diagnostic information to anoperator/installer. For example, the colour and/or brightness of lightemitted by the light source controlled so as to replay diagnosticinformation. Optionally, the light emitter could be configured to flashin particular ways so as to relay diagnostic information. Accordingly,for example, during setting up of the encoder, which could occur oninstallation or at a subsequent point (e.g. at a subsequent point itmight be necessary to setup the encoder again), the diagnosticinformation (e.g. the output of the light emitter) can be used by anoperator/installer to ensure that the encoder is properly set up. Inparticular, for those embodiments in which the scale signal receiver isarranged independently of the scale, the operator can use the diagnosticinformation to check whether the scale signal receiver has been arrangedat a desired position relative to the scale (in degrees of freedom otherthan that of the measuring dimension), and if not, then adjust thepositional relationship accordingly.

For example, the light emitter could be controlled so as to emit avisual signal that is dependent on the relative set up of the readhead(e.g. scale signal receiver) and the scale. This could be particularlyuseful during installation of the encoder module so as to confirm thatthe readhead is receiving a good signal from the scale. For instance,the encoder module could be configured such that the colour of the lightemitter 213 is dependent on the relative set up (e.g. green light couldbe emitted when the readhead is receiving a good/strong scale signal,and red light could be emitted when the readhead is receiving apoor/weak scale signal). Such a visual indication for indicating therelative set up of the readhead and scale can be useful for both“independently arranged” and “internally constrained” encoder modules.Such a visual indication for indicating the relative set up of thereadhead and scale can be particularly useful when (as mentioned above)an adjustment mechanism is provided for adjusting the relative set-upposition of the scale signal receiver with respect to the mountingblock.

In the embodiment described, the processor inside the mounting block 214that is used to determine a position is also configured to process theimage detected by the sensor 256 in order to determine the diagnosticinformation (however as will be understood this need not necessarily bethe case; a separate processor could be used). In the embodimentdescribed, the processor is configured to determine diagnosticinformation based on the quality of the signal detected by the sensor.In this particular embodiment, it is configured to Fourier Transform theimage obtained by the sensor at the fundamental spatial frequency, ω, ofthe scale's features (which could be provided during set up of theencoder module or by analysis of the image). The magnitude, A, of theFourier transform is then established. As will be understood, a Fouriertransform provides a real part

and an imaginary part ℑ, and the magnitude A can be calculated from thefollowing equation:A=√{square root over ([

(F(ω))]²+[ℑ(F(ω))]²)} or A ²=[

(F(ω))]²+[ℑ(F(ω))]²  (1)

-   -   where F(ω) represents the Fourier transform of the        representation at spatial frequency ω

Since computing a square root is computationally intensive, it will beunderstood that it may be preferable to use A² instead of A to determinethe setup indicator output. The method then comprises comparing the A(or A²) to threshold values to determine how to control the lightemitter 213. For example, when A (or A²) has a value below a thresholdthen the light emitter can be controlled to output red light and when A(or A²) has a value above a threshold then the light emitter can becontrolled to output green light.

As will be understood, A (or A²) is dependent on the amplitude of thefeatures as obtained in the representation. This is in turn affected bythe setup of the readhead relative to the scale (which is what is to bedetermined). A (or A²) is also dependent on the number of features inthe representation. Accordingly, if there is significant variation inthe density of features along the scale, then the method can comprisesteps to compensate for this. For example, this compensation may beachieved by dividing A (or A²) by the number of features in therepresentation.

In the described embodiment, the method involves Fourier Transformingthe representation substantially at the fundamental spatial frequency ofthe features. The Fourier Transform could use an assumed fundamentalspatial frequency of the features, based on the scale that it is beingused with. Even if the assumed fundamental frequency is not exactlycorrect, then the method can still provide a useful indication of thequality of the representation. Optionally, the fundamental spatialfrequency of the features could be determined by analysing the imagebefore performing the Fourier Transform. This could be useful inembodiments in which the actual fundamental spatial frequency of thefeatures as imaged varies significantly due to rideheight/magnificationeffects.

Furthermore, as will be understood, it need not necessarily be the casethat the Fourier Transform is performed substantially at the fundamentalspatial frequency of the features. For instance, the method couldinvolve performing the Fourier Transform at some other frequency, e.g.at a harmonic of the spatial frequency. Optionally, the method couldinvolve performing the Fourier Transform at one or more frequencies andcomparing the magnitude of the Fourier Transforms at the differentspatial frequencies.

Additional details of how an image of an absolute scale can be processedto determine diagnostic information is described in U.S. Pat. No.8,505,210, the content of which is incorporated herein by thisreference. As will be understood, there are other ways in which thediagnostic information can be determined. For example, as described inU.S. Pat. No. 8,505,210, the relative amplitude of different types ofscale features as imaged can be determined which can be indicative ofthe quality of the scale signal detected.

As shown, in this embodiment, the scale signal receiver 206 alsocomprises a vibration control device (in fact, this embodiment comprisesa plurality of vibration control devices), which in this particularembodiment comprises a tuned mass damper 260. Our inventors have foundthe use of at least one vibration control device can improve the lifeand/or metrological performance of an encoder apparatus. This isparticularly the case when the scale signal receiver is rigidly mountedto a structure via a member susceptible to vibration (e.g. a memberwhich transmits and/or amplifies vibration) such as an elongate arm or athin blade to which the scale signal receiver is rigidly mounted. Forexample, in the case of the “externally constrained” scale signalreceiver of the embodiments described above, vibrations are passedthrough to the scale signal receiver via the rigid mounting arrangement.A vibration control device provides a way of controlling such unwantedvibration to which the scale signal receiver is exposed.

As will be understood, a vibration control device can be a deviceconfigured to reduce the response of a system (e.g. the scale signalreceiver) due to external excitation. As mentioned above, in thisparticular example, the vibration control device comprises a tuned massdamper 260 which is tuned so as to reduce the amplitude of vibrations inthe system in which it is installed, at and around the system's resonantfrequency. As will be understood, a tuned mass damper comprises aspring, a damper and a mass. The spring's stiffness “k”, the damper'sdamping coefficient “c” and the mass's mass “m” are selected (in otherwords “tuned”) so as to reduce the amplitude of vibrations of the systemin which it is installed, at and around the system's resonant frequency.In this embodiment, the tuned mass damper comprises a pair of elastomerrings 262 (for example rubber rings), which provides the spring anddamper elements, and a body 264 which provides the mass element.Accordingly, each elastomer ring 262 acts as a spring and a damper, byway of absorbing energy and converting the energy to heat. The body 264comprises a sufficiently dense material (e.g. brass) so as to enable thebody 264 to have sufficiently small size whilst providing suitable highmass.

Typically, the mass of a tuned mass damper needs to be a substantialpercentage of the mass of the system it is intended to damp (in thiscase the parts of the readhead assembly located inside the protectivehousing, in particular the scale signal receiver 206). For example, inthis case, the mass of the tuned mass damper 260 can be at least 1% ofthe mass of the scale signal receiver 206, optionally at least 2% of themass of the scale signal receiver 206, for example approximately 5% ofthe mass of the scale signal receiver 206. For example, in this case,the mass of the tuned mass damper 260 could be configured such that itis not more than 30% of the mass of the scale signal receiver 206,optionally not more than 25% of the mass of the scale signal receiver206.

As shown in FIG. 4, the tuned mass dampers 260 are located insidecylindrical holes provided by the scale signal receiver 206. Althoughnot shown, in the particular embodiment described, the sides of thecylindrical holes comprises a plurality of elongate, axially extendingridges (or “splines”) such that the outer circumference of the elastomerrings 262 engages said ridges, thereby reducing the contact area betweenthe elastomer rings 262 and the inside of the hole. This helps to keepdown the stiffness of the elastomer rings 262, which in turn helps toreduce the natural frequency of the tuned mass dampers 260. Such aconfiguration avoids the need to use a greater mass 264 or softerelastomer rings 262 to obtain the desired damping effect.

As will be understood, the elastomer rings 262 and the cylindrical holein which the tuned mass dampers 260 are located could be shaped andsized such that the elastomer rings 262 are squashed/compressed withinthe holes. As will be understood, even in such a case, the mass element264 will move/vibrate around independently of the scale signal receiver206. Alternatively, the elastomer rings 262 and the cylindrical hole inwhich the tuned mass dampers 260 are located could be shaped and sizedsuch that the elastomer rings 262 are not squashed/compressed within theholes. Accordingly, the elastomer rings 262 and the cylindrical hole inwhich the tuned mass dampers 260 are located could be shaped and sizedsuch that the elastomer rings 262 are free to rattle/bounce aroundwithin the holes.

FIGS. 6a, 6b, 7a and 7b illustrate further alternative implementationsof suitable vibration control devices. With respect to FIGS. 6a and 6b ,the vibration control device comprises a mass element 364 connected tothe outer case 207 of the scale signal receiver 206 via a spring anddamper element 362. In this case the spring and damper element 362 is ablock of elastomer material, such as rubber. The mass element 364 istherefore able to vibrate independently of the scale signal receiver206, by virtue of the flexibility of the spring and damper element 362(which acts as a spring and a damper, by way of absorbing energy andconverting the energy to heat).

FIGS. 7a and 7b illustrate another alternative embodiment comprising atuned mass damper 460. In this case the tuned mass damper 460 comprisesa mass 464 formed as an integral part (e.g. via a single moulding) ofthe outer case 207 of the scale signal receiver 206. The tuned massdamper also comprises a spring element 466 which is also formed as anintegral part of the outer case 207 of the scale signal receiver 206. Asshown in the cross-sectional drawing of FIG. 7b , the material of thespring element 466 provided by the outer case 207 is sufficiently thinso as to be flexible enough to enable the mass 464 to move and vibraterelative to the rest of the scale signal receiver 206. In thisembodiment, a separate damping element 462 (shown in FIG. 7b ) isprovided, which comprises an elastomer ring 462 that extends around atrough in the outer case 207 resulting from the presence of theintegrally formed spring element 466.

As will be understood, FIGS. 6b and 7b also illustrate how that theblade 216 can be hollow for the passage of wires (not shown) and/or air(as explained above). These figures also show how that the mountingblock 214 can comprise space for components such as at least oneprocessor device 242 (as explained in more detail above).

As schematically illustrated by FIG. 8a , the spring and damper parts ofthe tuned mass damper need not be provided by a common part. Forexample, an example tuned mass damper 560, can comprise a mass 562, andone or more (in this case four) springs 566 (which have little or nosubstantial damping effect) and one or more (in this case four) dampingelements 564.

In the above described embodiments, the vibration control devicecomprises a tuned mass damper. However, as will be understood, this neednot necessarily be the case. For example, the vibration control devicecould comprise a vibration absorber 660, an example of which isillustrated in FIG. 8b . As schematically illustrated, a vibrationabsorber 660 can comprise a mass element 662, and one or more springs666 (in this example four springs 666) which enable the mass 662 tomove/vibrate independently of the outer case 207 and the rest of thescale signal receiving unit 206.

In the embodiments depicted in FIGS. 8a and 8b , the vibrationcontrollers 560, 660 are located in a recess provided in the outer case207 of the scale signal receiver 206, but as will be understood otherarrangements are possible. For example, as shown in FIG. 8c thevibration controller 770 (comprising a mass element 762, spring 766 andoptionally a damper element 764) could be connected to the side of theouter case 207 of the scale signal receiving unit 206.

In the above described embodiments, the encoder and scale are linear.However, as will be understood, the invention is equally applicable tonon-linear encoders/scale, for example rotary encoders such as discand/or ring encoders. FIGS. 9a, 9b, 10a and 10b schematically illustrateexample implementations of such embodiments. In the embodiment of FIG.9a , the scale 804 is provided on the face of a disc (shown as a dashedline) and is contained within a cylindrical protective housing 808. Acircular seal 811, through which the blade 216 of a readhead assemblycan pass, is provided on the end face of the cylindrical protectivehousing 808 (although as will be understood could be provided on thecylindrical side face of the cylindrical protective housing 808 ifdesired). In the embodiment of FIG. 9b , the scale 904 is provided onthe circumferential side of a ring (shown as a dashed line) and iscontained within a cylindrical protective housing 908. A circular seal911, through which the blade 216 of a readhead assembly can pass, isprovided on the cylindrical side face of the cylindrical protectivehousing 908 (although as will be understood could be provided on the endface of the cylindrical protective housing 908 if desired). In theseembodiments, the readhead assembly (comprising the scale signal receiver207, mounting block 214 and blade 216) can be the same as describedabove (although in the embodiment of FIG. 9a , it might be beneficialfor the blade to be curved to follow the curvature of the seal 811). Inboth these embodiments, a light emitter 213 is provided on the mountingblock 214 and the encoder is configured to control the light emitter torelay diagnostic information.

FIGS. 10a and 10b illustrate an alternative embodiment of a sealedrotary encoder module 302 according to the present invention. In thisembodiment, the sealed rotary encoder module 302 comprises (as bestshown in the cross-sectional FIG. 10b ) a scale 304 having a pluralityof features (not shown) and a readhead comprising a scale signalreceiver 306 for receiving a signal from the scale 304.

The scale 304 and scale signal receiver 306 are located inside aprotective housing 308 which protects them from contaminants external tothe protective housing. In this embodiment, the protective housingcomprises first 308 a and second 308 b parts. The scale signal receiver306 is mounted to the first part 308 a of the protective housing and thescale 304 is mounted to the second part 308 b of the protective housing.First and second sealing lips 312 provide a seal between the first 308 aand second 308 b parts whilst permitting relative movement of the first308 a and second 308 b parts of the protective housing about arotational axis A. Accordingly, for example, the second part 308 b ofthe protective housing can be mounted (e.g. clamped) to a rotatableshaft of a machine (not shown), and the first part 308 a of theprotective housing can be mounted (e.g. clamped) to a stationary part amachine (not shown).

As with the above described embodiments, the scale signal receiver 306comprises an outer case 307 within which the optical and electricalcomponents of the scale signal receiver are contained and protected.Also, as with the above described embodiment, the encoder module 302communicates with an external processor device (not shown), e.g. acontroller, via a communications channel which in the describedembodiment comprises a physical connection (e.g. cable 305). Inparticular, position signals can be transmitted to an external processordevice via the cable. In this embodiment, the scale signal receiver 306comprises the sensor and processor for detecting and processing thescale signal in order to form position information. However, as will beunderstood, another part of the encoder module 302 could comprise thesensor and/or processor (e.g. a separate component located elsewherealong the first part 308 a of the protective housing).

As with the above described embodiments, the sealed rotary module 302comprises a light emitter 313 for relaying diagnostic information to anoperator/installer. Such a light emitter 313 can be controlled by aprocessor (e.g. the same processor for processing the detected scalesignal) in accordance with the methods described above in connectionwith the other embodiments of the invention.

As with the above described embodiments, the encoder module 302comprises an optical absolute encoder, but this need not necessarily bethe case.

In the embodiments described above in connection with FIGS. 1 to 9, thereadhead assembly comprises a scale signal receiver 106, 206, mountingblock 114, 214 and a blade 116, 216. However, as will be understood, thereadhead assembly could comprise a scale signal receiver only. Forexample, the blade could be provided by the machine on which the scalesignal receiver is to be mounted. For example, in connection with theabove described embodiments, the sealed encoder module could be suppliedwithout a mounting block and/or blade, but rather just the scale signalreceiver which is (or is to be) located inside the protective housing.During set up, the scale signal receiver can be connected to a blade orequivalent which is provided by the machine on which the encoderapparatus is being installed.

In the above described embodiments, the encoder is a reflective opticalencoder (e.g. the readhead detects the scale by light reflected from thescale, and the readhead's light source and detector(s)/sensor(s) arelocated on the same side of the scale). As will be understood, theencoder could be a transmissive optical encoder (in which case thereadhead's light source and detector(s)/sensor(s) are on opposite sidesof the scale). As will also be understood, the invention is applicableto non-optical encoders (e.g. magnetic, inductive and/or capacitiveencoders).

As described above, the scale comprises features which are used toprovide a signal detectable by the readhead assembly's sensor. In theembodiments described above, the encoder/scale comprises an absoluteencoder/scale. The readhead decodes the image obtained to determine anabsolute position. However, this need not necessarily be the case. Forexample, the encoder/scale could be an incremental encoder/scale (withor without reference marks). As is well known, the readhead could beconfigured to output quadrature signals which can be used to determinerelative motion and/or position of the scale and readhead. In this case,an alternative technique could be used to determine diagnosticinformation that can be used to determine how to control the lightemitter 13, 113, 213. For example, the encoder module (e.g. thereadhead) could be configured to determine whether the quadrature signallevels are above or below given threshold levels to determine how tocontrol the light emitter 13, 113, 213. Further details of such aprocess are described in U.S. Pat. No. 5,241,173, the content of whichis incorporated herein by this reference.

The encoder could be diffraction-based, e.g. the signal detected by thescale sensor assembly's sensor is formed by the scale (and one or morediffraction gratings in the scale sensor assembly) diffracting light(e.g. forming an interference fringe at the scale sensor assembly'ssensor).

As will be understood, references to light in this application compriseelectromagnetic radiation (EMR) in the ultra-violet to infra-red range.

In the above described embodiments of FIGS. 2 to 9, a vibration controldevice is used to reduce the susceptibility of the scale signal receiverto vibrations. However, as will be understood, a vibration controldevice is optional. For example, the embodiment of FIG. 10 does notcomprise a vibration control device. There can be numerous reasons why avibration control device might not be needed. For example, a vibrationcontrol device might be unnecessary depending on the frequency of thevibration the encoder is to be exposed to and the resonant frequency ofthe scale signal receiver. Optionally, any vibrations induced in thescale signal receiver could be sufficiently small so as to not affectthe structural stability of the scale signal receiver and/or producemeasurement errors which are within desired tolerances. Furthermore, inthose embodiments of the invention in which the encoder apparatus is notindependently arranged with respect to the scale (e.g. comprises“integral bearings”), a vibration control device is unlikely to beneeded due to the scale signal receiver being biased against the scale.Such an example embodiment of the invention is described below inconnection with FIGS. 1a to 1 d.

The above described embodiments of FIGS. 2 to 10 comprise scale signalreceivers which are arranged independently of the scale. However, aswill be understood, the invention is also equally applicable to sealedencoder modules in which the scale signal receiver is not independentlyarranged with respect to the scale (e.g. which comprise “integralbearings”). Such an embodiment of the invention is described below inconnection with FIGS. 1a to 1 d.

In the above described embodiments, the scale signal receiver comprisesan outer casing which encapsulates the scale signal receiver components.However, this need not necessarily be the case. For example, theelectronic and/or other (e.g. optical) components could be exposed. Forexample, the PCB 240 could be exposed within the protective housing 108.Such an example embodiment of the invention is described below inconnection with FIGS. 1a to 1 d.

The above embodiments illustrate the way in which the invention of ansealed encoder apparatus being configured to determine and outputdiagnostic information concerning the scale signal, can be implementedin connection with a novel type of sealed encoder, (in particular inwhich the scale signal receiver is arranged within the protectivehousing independently of the scale; in other words, it is “externallyconstrained”). However, as will be understood, the invention of anenclosed encoder apparatus being configured to determine and outputdiagnostic information concerning the scale signal can also be used intraditionally configured sealed encoder apparatus, such as those inwhich the readhead is constrained relative to the scale, which could bedescribed as being “internally constrained” (e.g. an encoder such asthat described in U.S. Pat. No. 4,595,991).

An example of an “internally constrained”, “integral bearing” sealedencoder module 2 according to an aspect of the invention isschematically illustrated in FIGS. 1a to 1d . As illustrated, the sealedencoder module 2 comprises a scale 4 and a readhead assembly comprisinga scale signal receiver 6. The scale 4 and the scale signal receiver 6are located inside a protective housing 8 which protects them fromcontaminants external to the protective housing. The scale 4 is fixed tothe protective housing 8 whereas the scale signal receiver 6 of thereadhead assembly can move along the length of the scale 4 within theprotective housing 8. In use, the protective housing 8 will be securedto a first part of a machine (not shown) and the readhead assembly willbe secured to a second part of the machine, which is moveable relativeto the first part along the x axis. In practice, during use, the firstpart of the machine (and hence the protective housing/scale) could beconfigured to move, and/or the second part of the machine (and hence thereadhead) could be configured to move.

The readhead assembly comprises a mounting block 14 which is to bedirectly fastened to the second part of the machine (e.g. via boltspassing through bolt holes 15 in the mounting block 14), a blade 16 andan articulated linkage 18 which connects the scale signal receiver 6 tothe blade 16 (described in more detail below). A light emitter 13 forrelaying diagnostic information in the same manner as described inconnection with the above described embodiments is provided on themounting block.

The protective housing 8 further comprises a seal in the form of a pairof sealing lips 12 which seals the inside of the protective housing 8,in which the scale 4 and scale signal receiver 6 reside, from externalcontaminants. The blade 16 passes through the seal (between the pair ofsealing lips 12) and the sealing lips 12 allow the movement of the blade16 and hence the scale signal receiver 6 along the length of theprotective housing 8/scale 4.

The position of the scale signal receiver 6 relative to the scale 4 inall degrees of freedom other than along the length of the scale istightly controlled by bearings 20 (e.g. roller bearings) in the scalesignal receiver 6 which engage and bear against the scale 4 (but as willbe understood could additionally/alternatively bear against the insideof the protective housing). Springs (not shown) bias the scale signalreceiver's bearings 20 against the scale 4. Any misalignment in the axisof the first and second parts of the machine is accommodated by thearticulated linkage 18. In this embodiment, the articulated linkage 18is provided by a joint, which includes at least one pivot joint. Thearticulated linkage permits pitching, rolling and yawing (i.e.rotational movement about three mutually perpendicular axes) of thescale signal receiver 6 relative to the mounting block 14, as well aslateral motion of the scale signal receiver 6 relative to the mountingblock 14 in directions perpendicular to the measuring dimension (lengthof the scale). Accordingly, other than along the measuring dimension(along the x axis in the shown embodiment), the position and motion ofthe scale signal receiver 6 is constrained by the scale 4. In otherwords, the scale signal receiver 6 is guided by the scale 4. Thearticulated linkage 18 therefore decouples the scale signal receiver 6and mounting block 14 in all degrees of freedom other than along thedimension of measurement of the encoder apparatus (which should becoincident with the direction of motion the first and second parts ofthe machine), which in the embodiment shown in FIG. 1 is along the xaxis. As will be understood by a person skilled in the art, the way inwhich the readhead is constrained relative to the scale is known, forexample.

As also shown in FIG. 1b , a power/communications cable 5 can beprovided to enable the readhead assembly to be powered and facilitatecommunication between the readhead assembly and an external processordevice (e.g. a machine controller). Furthermore, an air supply line 9can be provided for supplying air into the protective housing 8, so asto create a positive pressure within the protective housing 8.Accordingly, in the case that the sealing lips 12 do not form a perfectseal (in particular where the lip seals are parted by the blade 16) airwill tend to flow out of the protective housing 8 due to the positivepressure. The positive pressure thereby provides further resistance tophysical contamination trying to enter the protective housing 8. As willbe understood such contamination can comprise solid and/or fluidcontamination, examples of which include swarf, liquid (e.g. coolant)and/or air-borne moisture. As also shown, another air supply line 7which supplies air into the protective housing via the readhead assembly(e.g. via a conduit passing through the mounting block 14 and blade 16)can be provided.

In the embodiments described, a light emitter 13, 113, 213, 313 isprovided on the encoder module for relaying diagnostic information. Inother embodiments, additionally or alternatively to such a light emitterbeing provided, the encoder module could be configured to determine andoutput diagnostic information in the form of one or more electronicsignals to an external device (e.g. a controller), for example via cable105, 205, 305. For instance, diagnostic information concerning thequality of the scale signal detected by the readhead could be determinedand output by the encoder module. The external device receiving thisinformation could, for example, display this information to an operator.Such diagnostic information could be useful to help an operatordetermine the status of the encoder module, e.g. to determine if theencoder module is operating properly and take action if it is not (e.g.stop the machine on which the encoder module is installed and/or replacethe encoder module).

In most of the embodiments described above, a light emitter 13, 113,213, is provided on the readhead. However, as will be understood, thisneed not necessarily be the case. For example, as illustrated in FIGS.1a, 1b and 1d , a light emitter 13′ could be provided on the protectivehousing 8. In this case, the protective housing 8 could comprise aninternal power source (e.g. a battery) for powering the light emitterand/or could be connected to an external power source. Furthermore, theprotective housing 8 could be configured to receive diagnosticinformation from the readhead in order to determine how to control thelight emitter. Optionally, the protective housing 8 is configured toreceive the scale signal detected by the readhead and is configured todetermine the diagnostic information itself in order to determine how tocontrol the light emitter. Either way, the protective housing couldcomprise its own processor device configured to determine how to controlthe light emitter (e.g. in response to the diagnostic received and/orsubsequent to it determining the diagnostic information itself).

As will be understood, the provision of a light emitter on theprotective housing is not exclusive to the type of encoder apparatusshown in FIGS. 1a to 1d but is equally applicable to the embodimentsdescribed above in connection with the other Figures. For example, asillustrated in FIGS. 2a, 2b, 9a and 9b a light emitter 113′, 213′ couldbe provided on the protective housing 108, 808, 908 in addition to orinstead of the readhead. Also, as described above, the embodiment FIG.10 comprises a light emitter 313 on the protective housing 308.

As will also be understood, a bracket (e.g. a “transit bracket”) or thelike can be used to keep the readhead assembly and the protectivehousing in a predetermined physical relationship, e.g. such as when theyare not mounted on a machine.

The invention claimed is:
 1. A sealed encoder module for mounting onto amachine so as to measure relative displacement of first and secondrelatively moveable parts of the machine, the sealed encoder modulecomprising: a scale; a readhead comprising a scale signal receiver; andan integral protective housing which encapsulates at least the scale andthe scale signal receiver, wherein: the sealed encoder module isconfigured to determine and output diagnostic information regarding ascale signal detected by the readhead; the sealed encoder module isconfigured to measure relative position of the scale and the scalesignal receiver in a first degree of freedom; and the diagnosticinformation is dependent on, and therefore indicative of, a relativepositional relationship of the scale and the scale signal receiver in atleast one degree of freedom other than in the first degree of freedom.2. The sealed encoder module as claimed in claim 1, wherein the readheadis configured to determine and output the diagnostic information.
 3. Thesealed encoder module as claimed in claim 1, comprising at least oneoutput device for outputting the diagnostic information as ahuman-detectable signal.
 4. The sealed encoder module as claimed inclaim 3, wherein the at least one output device comprises a visualoutput device.
 5. The sealed encoder module as claimed in claim 4,wherein the at least one output device is configured to emit an opticalsignal.
 6. The sealed encoder module as claimed in claim 3, wherein theat least one output device is provided on the readhead.
 7. The sealedencoder module as claimed in claim 3, wherein the readhead comprises amounting block external to the protective housing for mounting thereadhead to one of the first and second moveable parts of the machine,and wherein the at least one output device is provided on the mountingblock.
 8. The sealed encoder module as claimed in claim 3, wherein theat least one output device is provided on the protective housing.
 9. Thesealed encoder module as claimed in claim 1, wherein an arrangement ofthe scale signal receiver inside the protective housing is independentof the scale and the protective housing.
 10. The sealed encoder moduleas claimed in claim 1, wherein the protective housing comprises at leastone compliant sealing member through which the scale signal receiver canbe mounted to a part of the machine.
 11. The sealed encoder module asclaimed in claim 1, wherein the scale comprises a rotary scale.
 12. Thesealed encoder module as claimed in claim 11, wherein one of the scaleand the scale signal receiver (i) is mounted to a first part of theprotective housing which is configured to be mounted to a shaft of themachine, and (ii) is configured to be rotatable with respect to a secondpart of the protective housing to which the other of the scale and thescale signal receiver is attached, and wherein first and secondcompliant sealing rings are provided between the first and second partsof the protective housing on opposite sides of the one scale or scalesignal receiver.
 13. The sealed encoder module as claimed in claim 1,wherein the scale is an optical scale.
 14. The sealed encoder module asclaimed in claim 1, wherein the scale signal is used to determine themeasure of the relative displacement of the first and second parts ofthe machine.
 15. A machine comprising the sealed encoder moduleaccording to claim
 1. 16. A method of setting up a sealed encoder modulefor measuring relative displacement of first and second relativelymoveable parts of a machine, the sealed encoder module comprising: ascale; a readhead comprising a scale signal receiver; and an integralprotective housing which encapsulates at least the scale and the scalesignal receiver, wherein the sealed encoder module is configured todetermine and output diagnostic information regarding a scale signaldetected by the readhead, and wherein the sealed encoder module isconfigured to measure relative position of the scale and the scalesignal received in a first degree of freedom, the method comprising:using the diagnostic information to determine whether the scale and thescale signal receiver are in a desired relative positional relationshipin at least one degree of freedom other than the first degree offreedom.
 17. A sealed encoder module for mounting onto a machine so asto measure relative displacement of first and second relatively moveableparts of the machine, the sealed encoder module comprising: a scale; areadhead comprising a scale signal receiver and a mounting block formounting the readhead to one of the first and second moveable parts ofthe machine; and an integral protective housing which encapsulates atleast the scale and the scale signal receiver, wherein: the mountingblock is external to the integral protective housing; the sealed encodermodule is configured to measure a relative position of the scale and thescale signal receiver in a first degree of freedom; and the sealedencoder module comprises at least one visual output device provided onthe mounting block or on the integral protective housing and configuredsuch that the at least one visual output device outputs diagnosticinformation as an optical signal.
 18. The sealed encoder module asclaimed in claim 17, wherein the diagnostic information is dependent on,and therefore indicative of, a relative positional relationship of thescale and the scale signal receiver in at least one degree of freedomother than in the first degree of freedom.